Exciting new discoveries in phytochrome-mediated light signaling pathways
Exciting new discoveries in phytochrome-mediated light signaling pathways
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光敏色素介导的光信号通路的令人兴奋的新发现
DOI：
10.1016/j.scib.2023.05.008
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发表时间：
2023
期刊：
影响因子：
18.9
通讯作者：
Huq, Enamul
中科院分区：
文献类型：
--
作者：
Cai, Xingbo;Huq, Enamul
生物体如何感知周围环境并作出反应是生物学中的一个基本问题。这与植物特别相关，因为它们是无梗的。光和温度是对植物生长发育有深远影响的两个环境因子。植物已经进化出复杂的调节模块，将这些环境信号转化为它们的发育程序，从发芽到开花。光敏色素（Phytochromes）是一种普遍存在于从细菌到植物等生物体内的红/远红光感觉光感受器。光敏色素在黑暗中以红光吸收（Pr）形式存在，并在暴露于红光时转化为具有生物活性的红光吸收（Pfr）形式。在远红光照射下，Pfr形式可以转换回Pr形式，因此光敏色素的作用就像电灯开关一样，可以“开”和“关”。由于已知光敏色素存在于植物细胞的细胞质中，因此在70年代中期到90年代中期，光敏色素信号传导领域的主要焦点是寻找将光信号从细胞质传递到细胞核的第二信使。大量研究表明钙（Ca2+）、钙调素和cGMP参与介导光信号，控制基因表达和叶绿体发育[3]。然而，当一项里程碑式的研究表明光敏色素响应光[4]从细胞质转移到细胞核时，焦点迅速转移并保持在细胞核上。经过20多年对核光敏色素信号传导机制的关注，Zhao等人回到了细胞质Ca2+在介导光敏色素信号传导中的重要性，不是作为第二信使，而是作为光敏色素核易位的调节剂。Ca2+不仅作为一种矿物质，而且是一个复杂而复杂的信号通路网络的多功能调节剂，调节植物的生长、发育和胁迫反应[6,7]。在植物中，Ca2+信号是通过胞质中游离Ca2+，[Ca2+] cyt的变化介导的。不同刺激诱导的[Ca2+] cyt包括特定的周期和幅度，这些周期和幅度可以被Ca2+结合蛋白感知和解码，这些结合蛋白含有Ca2+结合结构域，如钙调蛋白。钙信号参与光转导[7]。红蓝光引起[Ca2+] cyt增加，Ca2+促进光响应基因表达[7]。然而，潜在的机制尚不清楚。Zhao等人的[5]填补了这一空白，并通过表征光敏色素B (phyB)-Ca2+-CPK6/12-phyB环来促进phyB在响应光信号时转运到细胞核中，从而架起了Ca2+信号通路和光敏色素信号通路的桥梁（图1）。他们表明，红光诱导黄化拟南芥幼苗中强健的[Ca2+] cyt增加，这是phyb依赖的。增加的[Ca2+] cyt激活两种钙依赖性蛋白激酶CPK6和CPK12，从而促进phyB在S80和S106位点的磷酸化。phyB核易位启动光响应需要S80/S106磷酸化。钙和光信号。Zhao等人的研究表明，短暂的红光照射（30秒）会导致[Ca2+] cyt的短暂增加，随后在2分钟内迅速下降到基础水平。然而，在phyB-9突变背景下，红光不能诱导[Ca2+] cyt增加，红光诱导[Ca2+] cyt在远红光下是可逆的，这表明phyB主要介导了对红光的[Ca2+] cyt诱导。类似地，蓝光也可以诱导[Ca2+] cyt增加，依赖于蓝光感光受体致光素，而不是隐色素[8]。蓝光暴露会引发Ca2+流入…
How organisms perceive and respond to their surrounding environment is a fundamental question in biology. This is particularly relevant to plants because of their sessile nature. Light and temperature are two environmental factors that have profound effects on plant growth and development. Plants have evolved intricate regulatory modules to translate these environmental signals into their developmental programs, from germination to flowering [1]. Phytochromes (phys) are one such red/far-red light sensory photoreceptors ubiquitously present in organisms ranging from bacteria to plants [2]. Phytochromes exist in the red light absorbing (Pr) form in darkness and are converted to a biologically active farred light absorbing (Pfr) form upon exposure to red light. The Pfr form can be converted back to Pr form upon far-red light exposure, thus phytochromes are acting like light switches that can be turned ‘‘on” and ‘‘off”. Because phytochromes were known to be in the cytosol in a plant cell, a major focus in the phytochrome signaling field in the mid-70s to mid-90s was to find second messengers that mediate the light signal from the cytoplasm to the nucleus. A number of research articles showed the involvement of calcium (Ca2+), calmodulin and cGMP in mediating light signaling to control gene expression and chloroplast development [3]. However, the focus quickly shifted and remained on to nucleus when a milestone study showed that phytochromes translocate from cytosol to the nucleus in response to light [4]. After more than two decades of intense focus on the nuclear phytochrome signaling mechanisms, Zhao et al.[5] circled back to the importance of cytosolic Ca2+ in mediating phytochrome signaling not as a second messenger but as a regulator of phytochrome nuclear translocation. Ca2+ not only acts as a mineral, but also is a versatile regulator of a complex and sophisticated network of signaling pathways, regulating plant growth, development, and stress responses [6, 7]. In plants, Ca2+ signals are mediated by changes in free cytosolic Ca2+,[Ca2+] cyt. Different stimulus-induced [Ca2+] cyt include specific periods and amplitude, which could be perceived and decoded by Ca2+-binding proteins, containing Ca2+ binding domains, like calmodulin. Calcium signaling is involved in phototransduction [7]. Red and blue light cause [Ca2+] cyt increase and Ca2+ promotes light-responsive gene expression [7]. However, the underlying mechanism is unclear. Zhao et al.[5] filled this gap and bridge the Ca2+ signaling and phytochrome signaling pathways by characterizing a phytochrome B (phyB)-Ca2+-CPK6/12-phyB loop to promote phyB translocation into the nucleus in response to light signals (Fig. 1). They show that red light induces a robust [Ca2+] cyt increase in etiolated Arabidopsis seedlings, which is phyB-dependent. The increased [Ca2+] cyt activates two calcium-dependent protein kinases, CPK6 and CPK12, which promote phyB phosphorylation at S80 and S106. S80/S106 phosphorylation is required for phyB nuclear translocation to initiate light responses. Calcium and light signaling. Zhao et al.[5] demonstrated short red light exposure (30 s) induces a transient increase in [Ca2+] cyt, followed by a rapid decay to basal level within 2 min. However, red light fails to induce [Ca2+] cyt increase in phyB-9 mutant background and [Ca2+] cyt induction by red light is reversible by far-red light, suggesting that phyB mainly mediates this [Ca2+] cyt induction in response to red light. Similarly, blue light can also induce [Ca2+] cyt increase relying on the blue light photoreceptor phototropin, rather than cryptochromes [8]. Blue light exposure triggers Ca2+ influx …